Microwave ablation instrument with flexible antenna assembly

ABSTRACT

A flexible microwave antenna assembly for a surgical ablation instrument capable of conforming to a tissue surface for ablation thereof. The ablation instrument includes a transmission line having a proximal portion suitable for connection to an electromagnetic energy source. The antenna assembly includes a flexible antenna coupled to the transmission line for radially generating an electric field sufficiently strong to cause tissue ablation. A flexible shield device is coupled to the antenna to substantially shield a surrounding area of the antenna from the electric field radially generated therefrom while permitting a majority of the field to be directed generally in a predetermined direction. A flexible insulator is disposed between the shield device and the antenna which defines a window portion enabling the transmission of the directed electric field in the predetermined direction. The antenna, the shield device and the insulator are formed for selective manipulative bending thereof, as a unit, to one of a plurality of contact positions to generally conform the window portion to the biological tissue surface to be ablated.

RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §120 as acontinuation of application Ser. No. 11/356,917, filed on Feb. 16, 2006,which is a division of application Ser. No. 10/219,598 filed on Aug. 14,2002, now abandoned, which is a continuation of application Ser. No.09/484,548, filed Jan. 18, 2000, now issued as U.S. Pat. No. 7,033,352,which applications are incorporated herein in the entirety by thisreference thereto.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates, generally, to ablation instrument systemsthat use electromagnetic energy in the microwave frequencies to ablateinternal bodily tissues, and, more particularly, to antenna arrangementsand instrument construction techniques that direct the microwave energyin selected directions that are relatively closely contained along theantenna.

2. Description of the Prior Art

It is well documented that atrial fibrillation, either alone or as aconsequence of other cardiac disease, continues to persist as the mostcommon cardiac arrhythmia. According to recent estimates, more than twomillion people in the U.S. suffer from this common arrhythmia, roughly0.15% to 2.0% of the population. Moreover, the prevalence of thiscardiac disease increases with age, affecting nearly 8% to 17% of thoseover 60 years of age.

Atrial arrhythmia may be treated using several methods. Pharmacologicaltreatment of atrial fibrillation, for example, is initially thepreferred approach, first to maintain normal sinus rhythm, or secondlyto decrease the ventricular response rate. Other forms of treatmentinclude chemical cardioversion to normal sinus rhythm, electricalcardioversion, and RF catheter ablation of selected areas determined bymapping. In the more recent past, other surgical procedures have beendeveloped for atrial fibrillation, including left atrial isolation,transvenous catheter or cryosurgical ablation of His bundle, and theCorridor procedure, which have effectively eliminated irregularventricular rhythm. However, these procedures have for the most partfailed to restore normal cardiac hemodynamics, or alleviate thepatient's vulnerability to thromboembolism because the atria are allowedto continue to fibrillate. Accordingly, a more effective surgicaltreatment was required to cure medically refractory atrial fibrillationof the heart.

On the basis of electrophysiologic mapping of the atria andidentification of macroreentrant circuits, a surgical approach wasdeveloped which effectively creates an electrical maze in the atrium(i.e., the MAZE procedure) and precludes the ability of the atria tofibrillate. Briefly, in the procedure commonly referred to as the MAZEIII procedure, strategic atrial incisions are performed to preventatrial reentry and allow sinus impulses to activate the entire atrialmyocardium, thereby preserving atrial transport functionpostoperatively. Since atrial fibrillation is characterized by thepresence of multiple macroreentrant circuits that are fleeting in natureand can occur anywhere in the atria, it is prudent to interrupt all ofthe potential pathways for atrial macroreentrant circuits. Thesecircuits, incidentally, have been identified by intraoperative mappingboth experimentally and clinically in patients.

Generally, this procedure includes the excision of both atrialappendages, and the electrical isolation of the pulmonary veins.Further, strategically placed atrial incisions not only interrupt theconduction routes of the common reentrant circuits, but they also directthe sinus impulse from the sinoatrial node to the atrioventricular nodealong a specified route. In essence, the entire atrial myocardium, withthe exception of the atrial appendages and the pulmonary veins, iselectrically activated by providing for multiple blind alleys off themain conduction route between the sinoatrial node to theatrioventricular node. Atrial transport function is thus preservedpostoperatively as generally set forth in the series of articles: Cox,Schuessler, Boineau, Canavan, Cain, Lindsay, Stone, Smith, Corr, Change,and D′Agostino, Jr., The Surgical Treatment Atrial Fibrillation (pts.1-4), 101 THORAC CARDIOVASC SURG., 402-426, 569-592 (1991).

While this MAZE III procedure has proven effective in ablating medicallyrefractory atrial fibrillation and associated detrimental sequelae, thisoperational procedure is traumatic to the patient since substantialincisions are introduced into the interior chambers of the heart.Consequently, other techniques have thus been developed to interrupt andredirect the conduction routes without requiring substantial atrialincisions. One such technique is strategic ablation of the atrialtissues through ablation catheters.

Most approved ablation catheter systems now utilize radio frequency (RF)energy as the ablating energy source. Accordingly, a variety of RF basedcatheters and power supplies are currently available toelectrophysiologists. However, radio frequency energy has severallimitations including the rapid dissipation of energy in surface tissuesresulting in shallow “burns” and failure to access deeper arrhythmictissues. Another limitation of RF ablation catheters is the risk of clotformation on the energy emitting electrodes. Such clots have anassociated danger of causing potentially lethal strokes in the eventthat a clot is dislodged from the catheter.

As such, catheters which utilize electromagnetic energy in the microwavefrequency range as the ablation energy source are currently beingdeveloped. Microwave frequency energy has long been recognized as aneffective energy source for heating biological tissues and has seen usein such hyperthermia applications as cancer treatment and preheating ofblood prior to infusions. Accordingly, in view of the drawbacks of thetraditional catheter ablation techniques, there has recently been agreat deal of interest in using microwave energy as an ablation energysource. The advantage of microwave energy is that it is much easier tocontrol and safer than direct current applications and it is capable ofgenerating substantially larger lesions than RF catheters, which greatlysimplifies the actual ablation procedures. Such microwave ablationsystems are described in the U.S. Pat. Nos. 4,641,649 to Walinsky;5,246,438 to Langberg; 5,405,346 to Grundy, et al.; and 5,314,466 toStern, et al, each of which is incorporated herein by reference.

Most of the existing microwave ablation catheters contemplate the use oflongitudinally extending helical antenna coils that direct theelectromagnetic energy in a radial direction that is generallyperpendicular to the longitudinal axis of the catheter although thefields created are not well constrained to the antenna itself. Althoughsuch catheter designs work well for a number of applications, such asradial output, they are inappropriate for use in precision surgicalprocedures. For example, in MAZE III surgical procedures, very preciseand strategic lesions must be formed in the heart tissue which theexisting microwave ablation catheters are incapable of delivering.

Consequently, microwave ablation instruments have recently beendeveloped which incorporate microwave antennas having directionalreflectors. Typically, a tapered directional reflector is positionedperipherally around the microwave antenna to direct the waves toward andout of a window portion of the antenna assembly. These ablationinstruments, thus, are capable of effectively transmittingelectromagnetic energy in a more specific direction. For example, theelectromagnetic energy may be transmitted generally perpendicular to thelongitudinal axis of the catheter but constrained to a selected angularsection of the antenna, or directly out the distal end of theinstrument. Typical of these designs are described in the U.S. patentapplication Ser. Nos. 09/178,066, filed Oct. 23, 1998; and 09/333,747,filed Jun. 14, 1999, each of which is incorporated herein by reference.

In these designs, the of the microwave antenna is preferably tunedassuming contact between the targeted tissue and a contact region of theantenna assembly extending longitudinally adjacent to the antennalongitudinal axis. Hence, should a portion of, or substantially all of,the exposed contact region of the antenna not be in contact with thetargeted tissue during ablation, the adaptation of the antenna will beadversely changed and the antenna will be untuned. As a result, theportion of the antenna not in contact with the targeted tissue willradiate the electromagnetic radiation into the surrounding air. Theefficiency of the energy delivery into the tissue will consequentlydecrease which in turn causes the penetration depth of the lesion todecrease.

This is particularly problematic when the tissue surfaces aresubstantially curvilinear, or when the targeted tissue for ablation isdifficult to access. Since these antenna designs are generallyrelatively rigid, it is often difficult to maneuver substantially all ofthe exposed contact region of the antenna into abutting contact againstthe targeted tissue. In these instances, several ablation instruments,having antennas of varying length and shape, may be necessary tocomplete just one series of ablations.

SUMMARY OF THE INVENTION

Accordingly, a flexible microwave antenna assembly is provided for asurgical ablation instrument adapted to ablate a surface of a biologicaltissue. The ablation instrument includes a transmission line having aproximal portion suitable for connection to an electromagnetic energysource. The antenna assembly includes a flexible antenna coupled to thetransmission line for radially generating an electric field sufficientlystrong to cause tissue ablation. A flexible shield device is coupled tothe antenna to substantially shield a surrounding area of the antennafrom the electric field radially generated therefrom while permitting amajority of the field to be directed generally in a predetermineddirection. A flexible insulator is disposed between the shield deviceand the antenna which defines a window portion enabling the transmissionof the directed electric field in the predetermined direction. Inaccordance with the present invention, the antenna, the shield deviceand the insulator are formed for selective manipulative bending thereof,as a unit, to one of a plurality of contact positions to generallyconform the window portion to the biological tissue surface to beablated.

In one configuration, a longitudinal axis of the antenna is off-set froma longitudinal axis of the insulator to position the antennasubstantially proximate to and adjacent the window portion. The shielddevice is in the shape of a semi-cylindrical shell having a longitudinalaxis generally co-axial with a longitudinal axis of the insulator.

In another embodiment, the insulator defines a receiving passage formedfor sliding receipt of the antenna longitudinal therein duringmanipulative bending of the antenna assembly. Moreover, a polyimide tubedevice may be positioned in the receiving passage proximate the distalend of the antenna. The tube provides a bore formed and dimensionedsliding longitudinal reciprocation therein of at least the distal end ofthe antenna.

Another embodiment of the present invention provides an elongated,bendable, retaining member adapted for longitudinal coupling therealongto the insulator. This bendable retaining member enables the insulatorto retain the one contact position after manipulative bending thereoffor the conformance of the window portion to the biological tissuesurface to be ablated. The retaining member is preferably disposedlongitudinally along the insulator, and on one the of the shield device,while the antenna is preferably disposed on an opposite side of theshield device, longitudinally along the insulator, and between theshield device and the window portion.

In another aspect of the present invention provides a microwave ablationinstrument, adapted to ablate a surface of a biological tissue, isprovided having a handle member formed for manual manipulation of theablation instrument. An elongated transmission line is provided coupledto the handle member. A proximal portion of the transmission line issuitable for connection to an electromagnetic energy source. Theablation instrument further includes a flexible antenna assembly coupledto the handle member which is formed for selective manipulative bendingthereof. The antenna assembly includes a flexible antenna coupled to thetransmission line for radially generating an electric field sufficientlystrong to cause tissue ablation. A flexible shield device of the antennaassembly is employed to substantially shield a surrounding radial areaof the antenna from the electric field radially generated therefrom,while permitting a majority of the field to be directed generally in apredetermined direction. A flexible insulator is disposed between theshield device and the antenna, and defines a window portion enabling thetransmission of the directed electric field in the predetermineddirection. The antenna, the shield device and the insulator are formedfor selective manipulative bending thereof, as a unit, to one of aplurality of contact positions to generally conform the window portionto the biological tissue surface to be ablated.

In this configuration, the ablation instrument may include a bendable,malleable shaft having a proximal portion coupled to the handle member,and an opposite a distal portion coupled to the antenna assembly. Theshaft is preferably a semi-rigid coaxial cable, but may also include atubular shaft where the transmission line may be disposed therethroughfrom the proximal portion to the distal portion thereof. The shaft ispreferably conductive having a distal portion conductively coupled tothe proximal end of the shield device, and another portion conductivelycoupled to the outer conductor of the transmission line.

In another embodiment, a restraining sleeve is adapted to limit thebending movement of the bendable antenna assembly at the conductivecoupling between the shield device and the shaft. The restraining sleeveis formed and dimensioned to extend peripherally over the conductivecoupling to limit the bending movement in a predetermined direction tomaintain the integrity of conductive coupling. The restraining sleeveincludes a curvilinear transverse cross-sectional dimension extendingpast the conductive coupling longitudinally therealong by an amountsufficient to maintain the integrity.

In still another configuration, an elongated grip member is includedhaving a distal grip portion and an opposite proximal portion coupled toa distal portion of the antenna assembly. The grip member and the handlemember cooperate to selectively bend the antenna assembly andselectively urge the window portion in abutting contact with thebiological tissue surface to be ablated. The gripping member ispreferably provided by an elongated flexible rod having a diametersmaller than a diameter of the insulator. A longitudinal axis of theflexible rod is off-set from the longitudinal axis of the insulator toposition the rod in general axial alignment with the antenna, andadjacent the window portion.

In still another aspect of the present invention, a method is providedfor ablating medically refractory atrial fibrillation of the heartincluding the step of providing a microwave ablation instrument having aflexible antenna assembly adapted to generate an electric fieldsufficiently strong to cause tissue ablation. The antenna assemblydefines a window portion enabling the transmission of the electric fieldthere through in a predetermined direction. The method further includesselectively bending and retaining the flexible antenna assembly in oneof a plurality of contact positions to generally conform the shape ofthe window portion to the targeted biological tissue surface to beablated, and manipulating the ablation instrument to strategicallyposition the conformed window portion into contact with the targetedbiological tissue surface. The next step includes forming an elongatedlesion in the targeted biological tissue surface through the generationof the electric field by the antenna assembly.

These bending, manipulating and generating events are preferablyrepeated to form a plurality of strategically positioned ablationlesions. Collectively, these lesions are formed to create apredetermined conduction pathway between a sinoatrial node and anatrioventricular node of the heart.

BRIEF DESCRIPTION OF THE DRAWINGS

The assembly of the present invention has other objects and features ofadvantage which will be more readily apparent from the followingdescription of the best mode of carrying out the invention and theappended claims, when taken in conjunction with the accompanyingdrawing, in which:

FIG. 1 is a diagrammatic top plan view of a microwave ablationinstrument system with a bendable directional reflective antennaassembly constructed in accordance with one embodiment of the presentinvention.

FIG. 2 is an enlarged, fragmentary, top perspective view of the antennaassembly of FIG. 1 mounted to a distal end of a handle member of theablation instrument.

FIG. 3 is an enlarged, fragmentary, top perspective view of the antennaassembly of FIG. 1 illustrated in a bent position to conform to asurface of the tissue to be ablated.

FIG. 4 is an enlarged, fragmentary, top perspective view of the antennaassembly of FIG. 2 illustrated in another bent position to conform to asurface of the tissue to be ablated.

FIG. 5 is an enlarged, fragmentary, top plan view of the antennaassembly of FIG. 2 illustrating movement between a normal position(phantom lines) and a bent position (solid lines).

FIG. 6 is a fragmentary side elevation view of the antenna assembly ofFIG. 5.

FIG. 7 is an enlarged, front elevation view, in cross-section, of theantenna assembly taken substantially along the plane of the line 7-7 inFIG. 6.

FIG. 8 is an enlarged, fragmentary, side elevation view of the antennaassembly of FIG. 2 having a restraining sleeve coupled thereto.

FIG. 9 is an enlarged, front elevation view, in cross-section, of theantenna assembly taken substantially along the plane of the line 9-9 inFIG. 8.

FIG. 10 is a diagrammatic top plan view of an alternative embodimentmicrowave ablation instrument system constructed in accordance with oneembodiment of the present invention.

FIG. 11 is a reduced, fragmentary, top perspective view of the antennaassembly of FIG. 10 illustrated in a bent position to conform to asurface of the tissue to be ablated.

FIG. 12 is a reduced, fragmentary, top perspective view of analternative embodiment antenna assembly of FIG. 10 having a flexiblehandle member.

DETAILED DESCRIPTION OF THE INVENTION

While the present invention will be described with reference to a fewspecific embodiments, the description is illustrative of the inventionand is not to be construed as limiting the invention. Variousmodifications to the present invention can be made to the preferredembodiments by those skilled in the art without departing from the truespirit and scope of the invention as defined by the appended claims. Itwill be noted here that for a better understanding, like components aredesignated by like reference numerals throughout the various Figures.

Turning now to FIGS. 1-4, a microwave ablation instrument, generallydesignated 20, is provided which is adapted to ablate a surface 21 of abiological tissue 22. The ablation instrument 20 includes a handlemember 23 formed to manually manipulate the instrument during opensurgery. An elongated transmission line 25 is provided coupled to thehandle member 23 at a distal portion thereof, and having a proximalportion suitable for connection to an electromagnetic energy source (notshown). The ablation instrument 20 further includes a flexible antennaassembly, generally designated 26, coupled to the handle member 23 andto the transmission line 25 to generate an electric field. The antennaassembly 26 is adapted to transmit an electric field out of a windowportion 27 thereof in a predetermined direction sufficiently strong tocause tissue ablation. The antenna assembly is further formed forselective manipulative bending to one of a plurality of contactpositions (e.g., FIGS. 3 and 4) to generally conform the window portion27 to the biological tissue surface 21 to be ablated.

More specifically, the flexible antenna assembly 26 includes a flexibleantenna 28 coupled to the transmission line 25 for radially generatingthe electric field substantially along the longitudinal length thereof.A flexible shield device 30 substantially shields a surrounding radialarea of the antenna wire 28 from the electric field radially generatedtherefrom, while permitting a majority of the field to be directedgenerally in a predetermined direction toward the window portion 27. Aflexible insulator 31 is disposed between the shield device 30 and theantenna 28, and defines the window portion 27 enabling the transmissionof the directed electric field in the predetermined direction. Theantenna 28, the shield device 30 and the insulator 31 are formed forselective manipulative bending thereof, as a unit, to one of a pluralityof contact positions to generally conform the window portion 27 to thebiological tissue surface 21 to be ablated.

Accordingly, the microwave ablation instrument of the present inventionenables manipulative bending of the antenna assembly to conform thewindow portion to the biological tissue surface to be ablated. Thisensures a greater degree of contact between the elongated window portionand the targeted tissue. This is imperative to maintain the radiationefficiency of the antenna, and thus, proper tuning for more efficientmicrowave transmission. Such manipulative bending also substantiallyincreases the versatility of the instrument since one antenna assemblycan be configured to conform to most tissue surfaces.

Briefly, the ablation instrument 20 includes a handle member 23 coupledto the antenna assembly 26 through an elongated tubular shaft orsemi-rigid coaxial cable, hereinafter referred to as shaft 32. Bymanually manipulating the handle, the window portion 27 of the antennaassembly 26 may be oriented and positioned to perform the desiredablation. As mentioned, the shaft 32 is preferably provided a semi-rigidcoaxial cable or by a conductive material such as a metallic hypotubewhich is mounted to the components of the antenna assembly 26 throughbrazing paste, welding or the like, as will be discussed. Accordingly,when the shaft 32 is provided by the semi-rigid coaxial cable, thebraided outer conductor 29 of the semi-rigid coaxial cable 32,peripherally surrounding the center conductor 33, is preferablyconductively coupled to the outer conductor of the transmission line 25.Similarly, the inner conductor 33 of the semi-rigid coaxial cable 32 isconductively coupled to the inner conductor of the transmission line 25.

In contrast, when the shaft 32 is provided by the tubular, such as aconductive hypotube, the solid cylindrical shell outer conductor 29thereof is preferably conductively coupled to the outer conductor of thetransmission line 25. In this configuration, the inner conductor and theinsulator of the transmission line extend through the cylindrical shellouter conductor 29 of the conductive hypotube 32 to provide the innerconductor 33 thereof. In this manner, the metallic hypotube itselffunctions as the outer conductor of the transmission line 25 forshielding along the length of the shaft.

Moreover, the shaft 32, whether the hypotube or the semi-rigid coaxialcable, is preferably bendable and malleable in nature to enable shapereconfiguration to position the antenna assembly at a desiredorientation relative the handle. This permits the surgeon toappropriately angle the window portion toward the targeted region fortissue ablation. It will be appreciated, however, that the material ofthe shaft 32 is further sufficiently rigid so that the shaft is noteasily deformed during operative use. Such materials for the hypotube,for example, include stainless steel or aluminum having diametersranging from about 0.090 inches to about 0.200 inches with wallthickness ranging from about 0.010 inches to about 0.050 inches. Whenthe semi-coaxial cable is applied as the shaft 32, the outer diameter ofthe outer conductor ranges from about 0.090 inches to about 0.200inches, with wall thickness ranging from about 0.010 inches to about0.050 inches; while the inner conductor includes a diameter in the rangeof about 0.010 inches to about 0.050 inches.

The transmission line 25 is typically coaxial, and is coupled to a powersupply (not shown) through connector 35 (FIG. 1). As best illustrated inFIGS. 2 and 5-7, the microwave ablation instrument 20 generally includesan elongated antenna wire 28 having a proximal end attached to centerconductor 33 of transmission line 25. These linear wire antennas radiatea cylindrical electric field pattern consistent with the length thereof.It will be appreciated, however, that the antenna may be any otherconfiguration, as well, such as a helical or coiled antenna.

The electrical interconnection between the antenna wire 28 and thedistal end of the center conductor 33 may be made in any suitable mannersuch as through soldering, brazing, ultrasonic welding or adhesivebonding. Moreover, the antenna wire 28 may be an extension of the centerconductor of the transmission line itself which has the advantage offorming a more rugged connection therebetween. Typically, the antennawire 28 is composed of any suitable material, such as spring steel,beryllium copper, or silver-plated copper.

As will be discussed in greater detail below, the diameter of theantenna wire may vary to some extent based on the particular applicationof the instrument. By way of example, an instrument suitable for use inan atrial fibrillation application may have typical diameter in therange of approximately 0.005 to 0.030 inches. More preferably, thediameter of antenna wire may be in the range of approximately 0.013 to0.020 inches.

The antenna 28 is designed to have a good radiation efficiency and to beelectrically balanced. Consequently, the energy delivery efficiency ofthe antenna is increased, while the reflected microwave power isdecreased which in turn reduces the operating temperature of thetransmission line. Moreover, the radiated electromagnetic field issubstantially constrained from the proximal end to the distal end of theantenna. Thus, the field extends substantially radially perpendicularlyto the antenna and is fairly well constrained to the length of theantenna itself regardless of the power used. This arrangement serves toprovide better control during ablation. Instruments having specifiedablation characteristics can be fabricated by building instruments withdifferent length antennas.

Briefly, the power supply (not shown) includes a microwave generatorwhich may take any conventional form. When using microwave energy fortissue ablation, the optimal frequencies are generally in theneighborhood of the optimal frequency for heating water. By way ofexample, frequencies in the range of approximately 800 MHz to 6 GHz workwell. Currently, the frequencies that are approved by the U.S. Food andDrug Administration for experimental clinical work are 915 MHz and 2.45GHz. Therefore, a power supply having the capacity to generate microwaveenergy at frequencies in the neighborhood of 2.45 GHz may be chosen. Aconventional magnetron of the type commonly used in microwave ovens isutilized as the generator. It should be appreciated, however, that anyother suitable microwave power source could be substituted in its place,and that the explained concepts may be applied at other frequencies likeabout 434 MHz, 915 MHz or 5.8 GHz (ISM band).

Referring back to FIGS. 1-5, the microwave ablation instrument 20 of thepresent invention will be described in detail. As above-mentioned, theantenna wire 28, the shield device 30 and the insulator 31 of theantenna assembly cooperate, as a unit, to enable selective manipulativebending thereof to one of a plurality of contact positions to generallyconform the window portion 27 to the biological tissue surface 21 to beablated. Thus, FIGS. 3 and 4 illustrate two particular contact positionswhere the window portion 27 may be configured to maintain contact forsubstantially curvilinear tissue surfaces 21. Consequently, due to theproper impedance matching between the medium of the insulator 31 andthat of the biological tissue, contact therebetween along the windowportion 27 is necessary to maintain the radiation efficiency of theantenna.

As above-mentioned, a flexible shield device 30 extend substantiallyalong the length of the antenna substantially parallel to thelongitudinal axis of the antenna in a normal unbent position (shown insolid lines in FIG. 2 and phantom lines in FIG. 5). The shield device 30is formed and dimensioned to shield selected surrounding areas radiallyabout the antenna wire 28 from the electric field radially generatedtherefrom, while reflecting the field and permitting the passage of thefield generally in a predetermined direction toward the strategicallylocated window portion 27 of the insulator 31. As best viewed in FIGS.2, 7 and 9, the shield device 30 is preferably semi-cylindrical orarcuate-shaped in the transverse cross-sectional dimension to reflectthe impinging field back toward the antenna thereof.

Tissue ablation can thus be more strategically controlled, directed andperformed without concern for undesirable ablation of other adjacenttissues which may otherwise be within the electromagnetic ablation rangeradially emanating from the antenna. In other words, any other tissuessurrounding the peripheral sides of the antenna which are out of line ofthe window portion of the cradle will not be subjected to the directedelectric field and thus not be ablated. This ablation instrumentassembly is particularly suitable for ablation procedures requiringaccurate tissue ablations such as those required in the MAZE IIIprocedure above-mentioned.

Briefly, it will be appreciated that the phrase “peripheral areaimmediately surrounding the antenna” is defined as the immediate radialtransmission pattern of the antenna which is within the electromagneticablation range thereof when the shield assembly is absent.

The shield device 30 is preferably composed of a high conductivity metalto provide superior microwave reflection. The walls of the shield device30, therefore, are substantially impenetrable to the passage ofmicrowaves emanating from the antenna 28 to protect a backside of theantenna assembly from microwave exposure. More specifically, when anincident electromagnetic wave originating from the antenna reaches theconductive shield device, a surface current is induced which in turngenerates a responsive electromagnetic field that will interfere withthat incident field. Consequently, this incident electromagnetic fieldtogether with the responsive electromagnetic field within the shielddevice 30 of the antenna assembly 26 cancel and are thus negligible.

FIGS. 2 and 5 best illustrate that the shield device 30 is preferablyprovided by a braided conductive mesh having a proximal end conductivelymounted to the distal portion of the outer conductor of the coaxialcable. This conductive mesh is preferably thin walled to minimize weightaddition to the shield assembly yet provide the appropriate microwaveshielding properties, as well as enable substantial flexibility of theshield device during bending movement. One particularly suitablematerial is stainless steel, for example, having mesh wires with athickness in the range of about 0.005 inches to about 0.010 inches, andmore preferably about 0.007 inches.

As mentioned, an elongated microwave antenna normally emits anelectromagnetic field substantially radially perpendicular to theantenna length which is fairly well constrained to the length of theantenna wire regardless of the power used. However, to assure propershielding, the longitudinal length of the shield may be longer than andextend beyond the distal and proximal ends of the antenna wire 28.

To maintain the electromagnetic field characteristics of the antennaduring operative use, even with a flexible antenna, it is important tomaintain the position of a transverse cross-sectional segment of shielddevice 30 relative a corresponding transverse cross-sectional segment ofthe antenna wire 28. Relative position changes between the segments mayalter the radiation pattern and the radiation efficiency of the antenna.Accordingly, to stabilize these transverse cross-sectional segments ofthe shield device relative to the corresponding transversecross-sectional segments of the antenna wire 28, the antenna assembly 26includes the flexible insulator 31 preferably molded over and disposedbetween the shield device 30 and the antenna wire 28.

The insulator 31 is preferably further molded to the distal portion ofthe metallic tubular shaft, and is preferably cylindrical shaped havingan axis generally coaxial with that of the shield device 30. Theinsulator 31 further performs the function of decreasing the couplingbetween the antenna 28 and the flexible shield device 30. Should theantenna 28 be too close to the conductive shield device 30, a strongcurrent may be induced at the surface thereof. This surface current willincrease the resistive losses in the metal and the temperature of thecradle device will increase. On the other hand, direct conductivecontact or substantially close contact of the antenna with the metalliccradle device will cause the reflective cradle device to become part ofthe radiative structure, and begin emitting electromagnetic energy inall directions.

The insulator 31 is therefore preferably provided by a good, low-lossdielectric material which is relatively unaffected by microwaveexposure, and thus capable of transmission of the electromagnetic fieldtherethrough. Moreover, the insulator material preferably has a lowwater absorption so that it is not itself heated by the microwaves.Finally, the insulation material must be capable of substantialflexibility without fracturing or breaking. Such materials includemoldable TEFLON®, silicone, or polyethylene, polyimide, etc.

In the preferred embodiment, the insulator 31 defines an elongatedwindow portion 27 extending substantially adjacent and parallel to theantenna wire 28. Thus, as shown in FIGS. 5 and 7-9, a longitudinal axisof the antenna wire 28 is off-set from, but parallel to, thelongitudinal axis of insulator 31 in a direction toward the windowportion. This configuration positions the antenna wire 28 actively inthe window portion 27 to maximize exposure of the targeted tissue to themicrowaves generated by antenna, as well as further space the antennasufficiently away from the shield device to prevent the above-mentionedelectrical coupling.

In a normal unbent position of the antenna assembly 26 (shown in solidlines in FIG. 2 and phantom lines in FIG. 5), the window portion 27 issubstantially planar and rectangular in shape. Upon bending thereof,however, the face of the window portion 27 can be manipulated togenerally conform to the surface of the tissue 22 to be ablated. Thus, agreater degree of contact of a curvilinear surface 21 of a tissue 22with full face of the window portion 27 is enabled. The radiationpattern along the antenna, therefore, will not be adversely changed andthe antenna will remain tuned, which increases the efficiency and thepenetration depth of the energy delivery into the tissue 22.

In accordance with the present invention, the window portion 27 isstrategically sized and located relative the shield device to direct amajority of the electromagnetic field generally in a predetermineddirection. As best viewed in FIGS. 2, 5 and 7, the window portion 27preferably extends longitudinally along the insulator 31 in a directionsubstantially parallel to the longitudinal axis thereof. The length ofthe ablative radiation is therefore generally constrained to the lengthof the antenna wire 28, and may be adjusted by either adjusting thelength of the antenna wire 28. To facilitate the coupling between thecoaxial cable and the antenna wire, the proximal end of the windowportion 27 generally extends proximally a little longer than theproximal end of the antenna 28 (about 2-5 mm). On the distal end,however, the window portion 27 is configured to approximate the lengthof the distal end of the shield device 30. Incidentally, as will bedescribed in greater detail below, the distal portion of the shielddevice 30 extends well beyond the distal end of the antenna toaccommodate for bending of the antenna assembly 26.

FIGS. 7 and 9 best illustrate that the radiation pattern of theelectromagnetic field delivered from the window portion 27 may extendradially from about 120° to about 180°, and most preferably extendradially about 180°, relative the longitudinal axis of the insulator.Thus, a substantial portion of the backside of the antenna is shieldedfrom ablative exposure of the microwaves radially generated by theantenna in directions substantially perpendicular to the longitudinalaxis thereof. The circumferential dimension of window portion 27, hence,may vary according to the breadth of the desired ablative exposurewithout departing from the true spirit and nature of the presentinvention. Moreover, while a small percentage of the electromagneticfield, unshielded by the shield device, may be transmitted out of othernon-window portions of the insulator, a substantial majority will betransmitted through the window portion. This is due to the impedancematching characteristics which are turned to contact between the tissueand the window portion.

Accordingly, the predetermined direction of the ablative electromagneticfield radially generated from the antenna may be substantiallycontrolled by the circumferential opening dimension, the length and theshape of the window portion 27. Manipulating the shape of the antennaassembly 26 to conform the window portion generally to the shape of thetargeted tissue surface, and positioning of window portion 27 in thedesired direction for contact with the tissue, thus, controls thedirection of the tissue ablation without subjecting the remainingperipheral area immediately surrounding the antenna to the ablativeelectromagnetic field.

In a preferred embodiment of the present invention, an elongated,bendable, retaining member, generally designated 36, is provided whichis adapted for longitudinal coupling therealong to the insulator 31.Once the window portion 27 is manually manipulated for conformance tothe biological tissue surface to be ablated, this bendable retainingmember 36 functions to retain the insulator 31 in the one position foroperative ablation thereof. As best viewed in FIGS. 2, 5 and 7, theretaining member 36 is preferably positioned behind the shield device 30so as to be shielded from exposure to the microwaves transmitted byantenna 28. The retaining member preferably extends along the fulllength of the shield device in a direction substantially parallel to thelongitudinal axis of the insulator 31.

This retaining member 36 must be a ductile or bendable material, yetprovide sufficient rigidity after being bent, to resist the resiliencyof the insulator to move from a bent position (e.g., FIGS. 3 and 4) backtoward the normal position (FIG. 2). Moreover, both the retaining member36 and the antenna wire 28 must not be composed of a material too rigidor brittle as to fracture or easily fatigue tear during repeated bendingmovement. Such materials for the retaining member include tin or silverplated copper or brass, having a diameter in the range of about 0.020inch to about 0.050 inches.

In a preferred form, retaining member 36 is molded or embedded in themoldable insulator. This facilitates protection of the retaining member36 from contact with corrosive elements during use. It will beappreciated, however, that retaining member 36 could be coupled to theexterior of the insulator longitudinally therealong.

As shown in FIGS. 2 and 5, a proximal portion of the retaining member 36is positioned adjacent and substantially parallel to a distal portion ofthe shaft 32. Preferably, the proximal portion of the retaining member36 is rigidly affixed to the distal portion of the shaft 32 at acoupling portion 41 thereof to provide relative stability between theshaft and the antenna assembly 26 during bending movement. While suchrigid attachment is preferably performed through soldering, brazing, orultrasonic welding, the coupling could be provided by a rigid,non-conductive adhesive or the like.

Preferably, the retaining member 36 is cylindrical-shaped, having asubstantially uniform transverse cross-sectional dimension. It will beappreciated, however, that other geometric transverse cross-sectionaldimensions may apply such as a rectangular cross-section. As shown inFIG. 9, this retaining member 36 is in the form of a thin metallic stripembedded atop the shield device 30. In this configuration, due to therelative orientation of the antenna and the shield device 30 bending invertical direction, will be permitted while movement in a lateralside-to-side direction will be resisted. Moreover, the retaining member36 may not be uniform in transverse cross-sectional dimension to permitvaried rigidity, and thus variable bending characteristics,longitudinally along the antenna assembly.

In another alternative configuration, the retaining member 36 may beincorporated into the shield device or the antenna itself. In either ofthese configurations, or a combination thereof, the shield device and/orthe antenna must provide sufficient rigidity to resist the resiliency ofthe insulator 31 to move from the bent position (e.g., FIGS. 3 and 4)back toward the normal position (FIG. 2).

In accordance with the present invention, the insulator 31 defines areceiving passage 37 formed for sliding receipt of the antenna wire 28longitudinally therein during manipulative bending of the antennaassembly 26. As best viewed in FIGS. 5 and 6, this sliding reciprocationenables bending of the antenna assembly 26 without subjecting theantenna 28 to compression or distension during bending movement of theantenna which may ultimately fatigue or damage the antenna, or adverselyalter the integrity of the electromagnetic field.

Such displacement is caused by the bending movement of the antennaassembly pivotally about the retaining member 36. For example, as shownin FIG. 7, during concave bending movement (FIGS. 2 and 5) or convexbending movement (FIG. 8) of the window portion 27 of the antennaassembly 26, the pivotal or bending movement will occur about thelongitudinal axis of the retaining member 36. Accordingly, upon concavebending movement of the window portion 27 (FIGS. 2 and 5), the length ofthe receiving passage 37 shortens. This is due to the fact that theinsulator 31 compresses at this portion thereof since the receivingpassage 37 is positioned along the radial interior of the retainingmember. Essentially, the radius of curvature of the receiving passage 37is now less than the radius of curvature of the outer retaining member36. However, the longitudinal length of the antenna 28 slideablyretained in the receiving passage 37 will remain constant and thus slidedistally into the receiving passage.

In contrast, upon convex bending movement of the window portion 27 (FIG.8), the length of the receiving passage 37 distends since the receivingpassage 37 will be positioned on the radial exterior of the retainingmember 36. In this situation, the radius of curvature of the receivingpassage 37 will now be greater than the radius of curvature of the outerretaining member 36. Consequently, the distal end of the antenna slidesproximally in the receiving passage 37.

Preferably, the diameter of the receiving passage is about 5% to about10% larger than that of the antenna wire 28. This assure uninterferedsliding reciprocation therein during bending movement of the antennaassembly 26. Moreover, the proximal end of the receiving passage 37 neednot commence at the proximal end of the antenna wire 28. For instance,since the displacement at the proximal portion of the antenna wire 28 issubstantially less than the displacement of the antenna wire 28 at adistal portion thereof, the proximal end of the receiving passage 37 maycommence about 30% to about 80% from the proximal end of the antennawire 28. The distal end of the receiving passage 37, on the other hand,preferably extends about 30% to about 40% past the distal end of theantenna wire 28 when the antenna assembly is in the normal unbentposition. As above-indicated, this space in the receiving passage 37beyond the distal end of the antenna 28 enables reciprocal displacementthereof during concave bending movement.

To assure that the distal end of the antenna 28 does not pierce throughthe relatively soft, flexible insulating material of the insulator 31,during bending movement, the tip portion thereof may be rounded orblunted. In another configuration, the receiving passage 37 may becompletely or partially lined with a flexible tube device 38 (FIGS. 2and 5-7) having a bore 39 formed and dimensioned for slidinglongitudinal reciprocation of the antenna distal end therein. The wallsof tube device 38 are preferably relatively thin for substantialflexibility thereof, yet provide substantially more resistance topiercing by the distal end of the antenna 28. Moreover, the materialcomposition of the tube device must have a low loss-tangent and lowwater absorption so that it is not itself affected by exposure to themicrowaves. Such materials include moldable TEFLON® and polyimide,polyethylene, etc.

Referring now to FIGS. 8 and 9, a restraining sleeve, generallydesignated 40, is provided which substantially prevents convex bendingmovement of the retaining member 36 at the proximal portion thereof. Atthis coupling portion 41, where the retaining member 36 and the shielddevice 30 are mounted to the distal portion of the shaft 32, repeatedreciprocal bending in the convex direction may cause substantial fatigueof the bond, and ultimately fracture. The restraining sleeve 40, thus,preferably extends longitudinally over the coupling portion 41 tomaintain the integrity of the coupling by preventing strains thereon.Essentially, such convex bending movement will then commence at aportion of the antenna assembly 26 distal to the coupling portion.

The restraining sleeve 40 includes an arcuate shaped base portion 42removably mounted to and substantially conforming with thecircumferential cross-sectional dimension of the proximal portion of theinsulator 31 (FIG. 9). The base portion 42 is rigidly affixed to theantenna assembly and/or the shaft to provide protective stability overthe coupling portion 41.

A finger portion 43 extends distally from the base portion 42 in amanner delaying the commencement of convex bending of the antennaassembly to a position past the distal end of the finger portion 43.Consequently, any strain upon the coupling portion 41 caused by convexbending movement of the antenna assembly is eliminated.

In another embodiment of the present invention, the microwave ablationinstrument 20 includes an elongated grip member 45 having a distal gripportion 46 and an opposite proximal portion 47 coupled to a distalportion of the antenna assembly 26. As best illustrated in FIGS. 10 and11, the grip member 45 and the handle member 23 of the ablationinstrument 20 cooperates to selectively bend the flexible antennaassembly 26 and selectively urge the window portion 27 into abuttingcontact with the biological tissue surface to be ablated. For example,this application is particularly useful when the targeted tissue surfaceis located at a rear portion of an organ or the like. FIG. 11illustrates that, during open procedures, the elongated grip member 45may be passed around the backside of the organ until the window portion27 of the antenna assembly is moved into abutting contact with thetargeted tissue surface 21. Subsequently, the handle member 23 at oneend of the ablation instrument, and the grip member 45 at the other endthereof are manually gripped and manipulated to urge the window portion27 into ablative contact with the targeted tissue surface.

This configuration is beneficial in that the window portion 27 isadapted to conform to the tissue surface upon manual pulling of the gripmember 45 and the handle member 23. As the flexible antenna assembly 26contacts the targeted tissue 22, the window portion 27 thereof is causedto conform to the periphery of the tissue surface. Continuedmanipulation of the grip member 45 and the handle member 23 further urgebending contact. Accordingly, this embodiment will not require aretaining member for shape retention.

The elongated grip member 45 is provided by a substantially flexible rodhaving a diameter smaller than the diameter of the insulator 31. Suchflexibility enables manipulation of the rod to position its distal endbehind a targeted biological tissue 22. Once the distal grip portion 46of the grip member 45 is strung underneath organ 22 or the like, thedistal grip portion 46 may be gripped to pull the antenna assembly 26behind the organ 22 for ablation of the targeted tissue.

It will be appreciated, however, that the rod 45 should not besubstantially more flexible than that of the antenna assembly. Thisassures that the window portion 27 of the insulator 31 will be caused toconform to the curvilinear surface of the targeted tissue 22, as opposedto the mere bending of the flexible rod 45. Such materials for theflexible rod 45 includes Pebax filled with silicone and polyethylene,polyurethane, etc.

To mount flexible rod 48 to the ablation instrument 20, the antennaassembly 26 includes a mounting portion 48 extending distally from theinsulator 31. This mounting portion 48 is preferably integrally formedwith the insulator 31 and is of a sufficient length to enable theproximal portion of flexible rod 45 to be integrally molded theretowithout interference with the shield device 30 and/or the antenna wire28.

In the preferred embodiment, a longitudinal axis of the flexible rod 45is off-set from the longitudinal axis of the insulator 31 in thedirection toward the window portion 27. As viewed in FIG. 11, thisoff-set preferably positions the longitudinal axis of the flexible rodproximately in co-axial alignment with the antenna. This arrangementfacilitates alignment of the window portion 27 against the targetedtissue 22 as the grip member 45 and the handle member 23 are manipulatedto conform the window portion 27 with and against the tissue surface 21.Due to the off-set nature of the flexible rod 45, when the antennaassembly and the rod are tightened around the biological tissue 22, theantenna assembly 26 is caused to rotate about its longitudinal axistoward an orientation of least resistance (i.e., a position where theflexible rod 45 is closest to the biological tissue 22).

Additionally, as shown in FIG. 12, the handle member 23 may be elongatedand substantially flexible in a manner similar to the elongated gripmember 45. In another embodiment of the present invention, the handlemember 23 includes a proximal grip portion 50 and an opposite distalportion 51 coupled to a proximal portion of the antenna assembly 26.Thus, the flexible handle member 23 and the flexible grip member 45cooperate to selectively bend the flexible antenna assembly 26 andselectively urge the window portion 27 into abutting contact with thebiological tissue surface to be ablated. As another example, thisapplication is particularly useful for creating long continuous linearlesions (E.g., to enclose the pulmonary veins when treating atrialfibrillation or the like). The flexible handle member 23 at one end ofthe ablation instrument, and the flexible grip member 45 at the otherend thereof are manually gripped and manipulated to urge the windowportion 27 into ablative contact with the targeted tissue surface. Thiscan be performed by simply sliding the antenna assembly 26 by pullingeither the flexible grip member 45 or the flexible handle member 23 toposition the window portion 27 against the tissue. Moreover, this can beused to slightly overlap the lesions to generate a long continuouslesion without gaps. easily end the targeted tissue surface is locatedat a rear portion of an organ or the like.

The elongated flexible handle member 23 is preferably provided by asubstantially flexible coaxial cable appropriately coupled to thetransmission line. In some instances, the handle member 23 may simply bean extension of the transmission line.

Preferably, the flexible coaxial cable handle member 23 is covered by aplastic sleeve such as Pebax, PE Polyolifin, etc. Such dual flexibilityenables increased manipulation of both the gripping member and thehandle member. To mount flexible handle member 23 to the antennaassembly 26, the distal portion thereof is preferably integrally formedwith the insulator.

Similar to the gripping member 45, a longitudinal axis of the flexiblehandle member 23 is off-set from the longitudinal axis of the insulator31 in the direction toward the window portion 27. As viewed in FIG. 12,this off-set, together with the same off-set of the gripping member,preferably positions the longitudinal axis of the handle memberproximately in co-axial alignment with the antenna. This arrangementfacilitates alignment of the window portion 27 against the targetedtissue 22 as the grip member 45 and the handle member 23 are manipulatedto conform the window portion 27 with and against the tissue surface 21.Due to the off-set nature of the flexible rod 45, when the antennaassembly and the rod are tightened around the biological tissue 22, theantenna assembly 26 is caused to rotate about its longitudinal axistoward an orientation of least resistance (i.e., a position where theflexible rod 45 is closest to the biological tissue 22).

In still another aspect of the present invention, a method is providedfor treatment of a heart including providing a microwave ablationinstrument 20 having a flexible antenna assembly 26 defining a windowportion 27 enabling the transmission of a directed electric fieldtherethrough in a predetermined direction. By selectively bending theflexible antenna assembly 26 to one of a plurality of contact positions,the window portion 27 can be generally conformed to the shape of thetargeted biological tissue 22 surface to be ablated. The method furtherincludes manipulating the ablation instrument 20 to strategicallyposition the conformed window portion 27 into contact with the targetedbiological tissue surface 21; and generating the electric fieldsufficiently strong to cause tissue ablation to the targeted biologicaltissue surface 21.

More preferably, this method is directed toward medically refractoryatrial fibrillation of the heart. By repeating the bending, manipulatingand generating events, a plurality of strategically positioned ablationlesions can be accurately formed in the heart. Collectively, theselesions are formed to create a predetermined conduction pathway betweena sinoatrial node and an atrioventricular node of the heart, or todivide the left and/or right atrium in order to avoid any reentrycircuits.

These techniques may be preformed while the heart remains beating, suchas in a minimally invasive heart procedure, while the heart istemporarily arrested, such as when the heart is stabilized for about 20or 30 seconds during a cabbage procedure, or while the heart isarrested, such as in an open heart surgery. Moreover, these proceduresmay be applied to ablate the endocardium as well as the epicardium inorder to treat atrial fibrillation. throughout the bending, manipulatingand generating events. Moreover, the repeated events of bending,manipulating and generating are applied in a manner isolating thepulmonary veins from the epicardium of the heart.

Although only a few embodiments of the present inventions have beendescribed in detail, it should be understood that the present inventionsmay be embodied in many other specific forms without departing from thespirit or scope of the inventions. Particularly, the invention has beendescribed in terms of a microwave ablation instrument for cardiacapplications, however, it should be appreciated that the described smalldiameter microwave ablation instrument could be used for a wide varietyof non-cardiac ablation applications as well.

It should also be appreciated that the microwave antenna need not be alinear antenna. The concepts of the present invention may be applied toany kind of radiative structure, such as a helical dipole antenna, aprinted antenna, a slow wave antenna, a lossy transmission antenna orthe like. Furthermore, it should be appreciated that the transmissionline does not absolutely have to be a coaxial cable. For example, thetransmission line may be provided by a stripline, a microstrip line, acoplanar line, or the like.

1. An ablation device for forming a lesion in targeted biologicaltissue, the device comprising: an ablation portion for deliveringablation energy to targeted biological tissue; a handle portionextending proximally of the ablation portion; and a grip portionattached to and extending distally from a distal end of the ablationportion to facilitate manipulating the ablation portion into positionrelative to the targeted biological tissue.
 2. The ablation deviceaccording to claim 1 in which the ablation portion and grip portion areflexible to facilitate conforming the ablation portion to contours ofthe targeted biological tissue.
 3. The ablation device according toclaim 1 in which the targeted biological tissue includes epicardialtissue and the ablation portion and grip portion are flexible tosubstantially conform to the surface contours of the targeted epicardialtissue.
 4. The ablation device according to claim 1 in which theablation portion includes a high frequency antenna structure fordelivering high frequency ablation energy to targeted biological tissuein response to high frequency energy applied to the antenna structure.5. The ablation device according to claim 1 in which the ablationportion delivers ablation energy through a window portion in a surfaceof the ablation portion; and the grip portion attached to a distal endof the ablation portion is axially offset in a direction toward thewindow portion.
 6. The ablation device according to claim 2 in which thehandle portion is flexible.